Key Technologies of Mobile IPv6

I. Introduction

With the rapid development of network technology and wireless communication devices, people are eager to obtain information from the Internet anytime and anywhere. In response to this situation, the Internet Engineering Task Force (IETF) began to develop a protocol supporting the mobile Internet in 1996, that is, the Mobile IP Protocol [1]. The Mobile IP protocol is a network layer solution that provides mobile functions on the Internet, so that nodes do not interrupt ongoing communication when switching the link. In particular, Mobile IP provides an IP routing mechanism that allows mobile nodes to connect to any link with a permanent IP address.

In order to achieve wireless access over the Internet, each mobile node must be assigned a globally unique TP address. However, due to the surge in the number of Internet users and new application requirements, IPv4 protocol has serious problems such as address shortage and insufficient support for network security and service quality, it cannot meet the needs of future network applications and development.

To this end, IETF has developed the Next Generation Internet Protocol IPv6. IPv6 inherits many features of IPv4, and its huge address space can meet the rapid development of the Internet. It also integrates content such as mobility, security, and service quality. Therefore, IPv6 Protocol [2] is urgently needed on the mobile Internet.

Ii. Mobile IPv6

1 Basic concepts of Mobile IPv6

* Mobile Node: a Node in Mobile IPv6 that can be moved from a connection point of a link to another connection point and can still be accessed through its home address.

* Home Agent: A router on the Home link of a mobile node. When a mobile node leaves his hometown, can the target address of his hometown link be intercepted? Group of the home address of the mobile node, which is forwarded to the transfer address registered by the mobile node through tunnel.

* Correspondent Node: All nodes that communicate with mobile nodes.

* Home Address: a permanent IP Address assigned to a mobile node. It belongs to the Home link of a mobile node. The standard IP routing mechanism sends the Group sent to the mobile node's home address to its home link. When a mobile node has multiple home subnet prefixes on the home link, it can have multiple home addresses.

* Care 0f Address: the IP Address obtained when a mobile node accesses a link in another region. The subnet prefix of this IP address is a foreign subnet prefix. The mobile node can get multiple forwarding addresses at the same time. The forwarding address registered with the home agent is called the primary forwarding address.

* Home Link: A Link corresponding to the Home subnet prefix of a mobile node.

* Foreign Link: Any Link except the home Link.

* Binding: the association between the home address and the transfer address of a mobile node.

2. Working Mechanism of Mobile IPv6

Compared with mobile IPv4, mobile IPv6 has great advantages, so it does not need to be a foreign proxy. It avoids the triangle routing problem, achieves route optimization, and better supports the mobility of mobile nodes.

When a mobile node is located in a home network, it works like a host with a fixed position. The Mobile IP address does not need to perform any special operations. When a mobile node leaves its hometown network and enters a foreign network, its working principle is as follows:

(1) A mobile node obtains one or more forwarding addresses through the conventional IPv6 stateless or stateful automatic configuration mechanism.

(2) After obtaining the transfer address, the mobile node applies to the home agent for registration, and establishes a binding relationship between the home address and the transfer address of the mobile node on the home agent.

(3) A mobile node can directly send a group to the communication peer, and set the source address of the Group to the current transfer address of the mobile node. The Home address option is the home address of the mobile node.

(4) When the communication peer sends a group to a mobile node, it first queries its binding cache based on the target IP address of the group. If a match exists in the binding, it directly sends the group to the mobile node. If such a match does not exist, the group is sent to its hometown address. The group sent to the home address is routed to the home link of the mobile node, and then forwarded to the mobile node through the home proxy tunnel.

(5) the mobile node determines that the communication peer does not have its own binding cache based on the IPv6 Group forwarded by the home proxy. Therefore, it sends binding updates to the communication peer to establish binding.

(6) After the mobile node leaves his hometown, the home network may be reconfigured, and the original home proxy will be replaced by other routers. Mobile IPv6 provides a "dynamic proxy address discovery" mechanism that allows mobile nodes to discover the IP address of the home proxy, so as to correctly register its primary forwarding address. Mobile IPv6 technology allows mobile nodes to roam over the Internet without changing their IP addresses. However, due to the instability of the Wireless Access environment, in order to ensure that mobile nodes can communicate with the peer end without interruption, the same quality of network service as fixed access is achieved, mobile IPv6 also needs to address the following key technologies.

Iii. Key Technologies of Mobile IPv6

1 mobile IPv6 switching technology [3]

When a mobile node moves from one subnet to another, it needs to be switched over ). Due to the high bit error rate and dynamic signal strength of wireless links, switching may prevent mobile nodes from receiving and sending data groups. In order to reduce the impact of switching on service quality, mobile IPv6 defines basic processes such as mobile detection, transfer address acquisition, and re-binding, and proposes several major switching schemes.

(1) fast switchover means low latency and is an extension of the Mobile IPv6 protocol. It adopts two mechanisms: Pre-switch and tunnel-based switch. By registering in advance and maintaining communication with the previous network when the new foreign network switch is not completed, the system implements fast switch. Pre-switching means that when the mobile nodes and the old Access Router (oAR, old Access Router) are still connected to the second layer, the mobile node or oAR can predict that the mobile node will enter a new network and initiate a layer-3 switch between the mobile node and the new Access Router. Tunnel-based switching means that layer-3 switching does not occur when a mobile node is connected to a new network and a layer-2 connection is established. OAR and nAR perform layer-2 switching between the two and establish a bidirectional tunnel using the information provided in the switching message. The mobile node can receive data from the previous network through the tunnel, minimize the interruption time of real-time streams.

(2) smooth switching the so-called smooth switching is a scheme proposed to reduce IP packet loss rate. When a mobile node is moved to a new network, a large number of IP data packets are often lost because the original data packets have not been sent. Therefore, mobile IPv6 proposes a caching mechanism. A mobile node requires the router of the current subnet to cache its data packets, knowing that the mobile node has completed the registration process for the new vro in the network. Once the registration is completed, the mobile node has a valid forwarding address in the new network, and cached packets are forwarded from the previous router, this greatly reduces the possibility of packet loss during the movement process.

2 QoS of Mobile IPv6 [4]

With the rapid growth of the Internet, the existing Internet provides the Best-effort service, which cannot meet many new application requirements. Therefore, QoS Assurance Technology must be supported on the Internet. To solve the IP QoS problem, IETF puts forward several Service models and mechanisms, mainly including: Integrated Services (IntServ, Integrated Service), Differentiated Services (DiffServ, Differentiated Service ), multi-Protocol Label Switching (MPLS, MuItiProtocol Lable Switch. However, these studies are based on fixed networks.

Mobile Internet will bring many new problems to QoS research, such as wireless communication quality, mobile management, and battery life. These factors impose higher requirements on QoS Assurance in Mobile IP networks. Therefore, QoS implementation in Mobile IP networks is much more complex than that in fixed IP networks. When a mobile node changes the network connection point, the intermediate network management domain of the Data Group may change. Therefore, QoS support information must be included in the data group of a mobile node, allowing the mobile node to establish and maintain reserved resources on the current path. The implementation of this protocol needs to modify and extend the RSVP protocol.

However, it is difficult to ensure IntServ QoS because it is a stream-based, complex Resource Reservation, QoS routing, and scheduling mechanism. Because the link status in a large-scale network is unstable, it is very difficult to reserve valid resources. At the same time, because the complexity of stream-based operations increases with the increase in the number of transmitted streams, IntServ is facing the expansion problem. Although DiffServ has good scalability, it cannot provide accurate service guarantee. Due to the lack of end-to-end signaling transmission, it does not support explicit acceptance control and dynamic resource management, this makes it difficult to adapt to QoS requirements in mobile environments. To support end-to-end QoS, IntServ and DiffServ can be combined to collaborate with each other to achieve scalability similar to the State-independent network and provide powerful QoS Assurance. At present, how to better combine these two technologies to provide QoS Assurance for Mobile IPv6 networks is a hot topic of research.